The invention relates to a process to produce an in-situ generated glassy coating on a non-oxide sintered ceramic fiber such as silicon carbide, boron carbide, or titanium boride. The coated fibers produced by the process in the case of sintered non oxide fibers, this invention have high tensile strength.
Non-oxide ceramic materials have high performance potential and are being used for high temperature advanced composites and insulation. However, silicon carbide fibers and other non-oxide ceramic fibers are susceptible to surface damage during processing causing a decrease in the fibers performance and tensile strength. The surface damage is generally seen as surface irregularities and in the case of sintered non-oxide fibers, protruding grains which are strength limiting to the fibers.
Tensile properties of glass and other ceramic fibers have generally been improved by applying an organic spin finish after forming and prior to contact with other fibers in a bundle or tow. The spin finish is designed to prevent formation of minute scratches and other contact type defects to the fibers. This method is not desirable for green non-oxide ceramic fibers that are to to be sintered because the finish would burn off during sintering.
There is a need to improve the performance and tensile strength of non-oxide ceramic fibers if they are to be used to their fullest potential. It is desirable to find a way to increase the strength and performance of sintered non-oxide ceramic fibers by coating the fiber.
It is object of the instant invention to produce a protective coating for non-oxide sintered fibers generated by an in situ chemical reaction. It is another object of the instant invention to improve the performance of sintered non-oxide ceramic fibers by coating the fiber with a glassy coating to fill in the surface irregularities and improve the strength and performance of the fiber.